Description
A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion. When a client is configured with a wildcard redirect URI, an attacker can use this to inject duplicate security parameters into the login response. If a client application is not configured correctly, it might trust the attacker's injected data instead of the real security information from Keycloak, leading to session fixation or account confusion.
Affected products
redhat: build of keycloak
References4
- access.redhat.com/security/cve/CVE-2026-18209 Vendor Advisory
- bugzilla.redhat.com/show_bug.cgi?id=2508305 Issue TrackingVendor Advisory
- access.redhat.com/errata/RHSA-2026:68277
- access.redhat.com/errata/RHSA-2026:68278
Metrics
- CVSS 3.1
-
4.7
MEDIUM
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N - EPSS — exploit probability
- 0% percentile: 36 · as of 13 November 2026
- CWE
- CWE-1288
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